1. Field of the Invention
Aspects of the present invention relate to a battery management system.
2. Description of the Related Art
In general, conventional vehicles having only an internal combustion engine are considered to be one of the primary causes of environmental pollution. Accordingly, in recent years, in order to decrease environmental pollution, attempts to develop electric vehicles and hybrid vehicles have been actively undertaken.
An electric vehicle has an electric motor that is powered by a battery pack including a plurality of rechargeable secondary. Since an electric vehicle uses a battery pack as a main power source, exhaust gas is not generated and little noise is produced.
A hybrid vehicle is an intermediate stage between a conventional internal combustion engine vehicle and an electric vehicle. A hybrid vehicle uses two or more power sources, for example, an internal combustion engine and a battery-powered motor. At the present time, a hybrid vehicle that uses an internal combustion engine and a fuel cell, where electrical energy is directly generated by chemically reacting hydrogen and oxygen, and a hybrid vehicle that uses a battery pack and a fuel cell, are being developed.
The number of secondary cells in a battery pack is increasing, in order to improve the power output thereof. Therefore, a cell balancing control method that can efficiently manage a plurality of connected cells in such battery packs is needed in a battery management system (hereinafter referred to as BMS).
When a battery pack includes a plurality of cells that are connected in series, balancing the cells is important. Such balancing refers to minimizing a difference between the voltages of the cells, to within an allowable range. Hereinafter, the balancing of the cells is referred to as “cell balancing.” Cell balancing is closely connected with the life-span and power output of a battery pack. A cell where the cell balancing does not occur deteriorates, shortening the life-span of the battery pack, and reducing the power output thereof.
The cell balancing is generally performed without regard to whether the cell voltages of cells are being measured. However, since the cell balancing and the cell voltage measurement are both performed through an electric line that is connected to the cells, if the cell balancing and the cell voltage measurement are simultaneously performed, they may interfere with each other. That is, when a cell voltage of a cell is checked, while the cell is being balanced, a voltage drop is generated by resistance of an electric line, resulting in a measured cell voltage that is lower than the actual cell voltage. Further, when the voltage of an adjacent cell that shares the electric line is measured, the measured voltage is higher than the actual cell voltage.
Specifically, referring to FIG. 1, a problem according to the related art will be described in detail. FIG. 1 is a diagram illustrating a waveform of a cell voltage measurement that is generated when cell balancing is performed, in a battery management system according to the related art. FIG. 1 shows a cell voltage waveform of a first cell of a plurality of cells of a battery system. Two cells that are adjacent to opposing sides of the first cell are referred to as a second cell and a third cell. The third, first, and second cells are sequentially arranged, close to a ground terminal.
As shown in FIG. 1, at a point of time T1, cell balancing of the second cell starts. Then, if a voltage of the first cell is measured, the voltage of the first cell increases, due to a current that is generated while the second cell is balanced, and due to the internal resistance of an electric line that is shared by the first cell and the second cell. At time T2, if the cell balancing of the first cell starts, the voltage of the first cell decreases, due to a voltage drop generated by the internal resistance of an electric line that is connected to the first cell. At this time, the voltage of the third cell, which shares an electric line with the first cell, increases. At time T3, if the cell balancing of the first cell is completed, the voltage of the third cell is measured as an actual voltage. At time T4, if the cell balancing of the second cell is completed, the voltage of the first cell is also measured as an actual voltage.
As such, the battery management system according to the related art has problems, in that the cell balancing and the cell voltage measurement are simultaneously performed, resulting in a measured cell voltage that is different from an actual cell voltage, due to the cell balancing of the adjacent cell.